Hot-melt pressure-sensitive adhesive for hygiene applications

ABSTRACT

The present invention relates to a pressure-sensitive hot-melt adhesive composition characterized in that it includes a) at least one ethylene-alkyl acrylate copolymer, b) a tackifying resin and c) optionally a diluent and/or a stabilizer and/or a wax. Such a composition may be employed advantageously in the field of hygiene, especially for the adhesive bonding of disposable nappies and of catamenial liners.

This application is the National Phase of International PatentApplication PCT/FR96/01424, filed Sep. 13, 1996, which claims priorityto French Patent Application 95.11252, filed Sep. 26, 1995, the entirecontents of each are hereby incorporated by reference in their entiretyand relied upon.

FIELD OF THE INVENTION

The present invention relates to a pressure-sensitive hot-melt adhesivecomposition, to its use in the field of hygiene and to the adhesivelybonded articles thus obtained, especially disposable nappies or diapersand catamenial liners.

BACKGROUND OF THE INVENTION

Disposable nappies generally consist of an absorbent filler protected onits outer face by a liquidproof polyethylene film and covered internallywith a film of nonwoven fabric, generally of polyethylene, which comesinto contact with the skin and allows body fluids to flow towards thesaid filler. More elaborate nappies may, in addition, contain aleakproof barrier of polyolefinic nature and/or an elastic waistband.

The nappies are conventionally prepared by adhesively bonding thevarious constituents with the aid of hot-melt adhesives whosecomposition can vary depending on the chemical nature of the componentsto be assembled. Such adhesives are described, for example, in thedocuments which follow.

U.S. Pat. No. 4,526,577 proposes an adhesive including a block copolymerA-B-A (in which A denotes a nonelastomeric block, for example styrene,and B denotes butadiene or hydrogenated butadiene), a compatibletackifying resin, a plasticizing oil and a stabilizer and, optionally, awax originating from petroleum.

U.S. Pat. No. 4,460,728 describes an adhesive based on an ethylene-vinylacetate or alkyl acrylate copolymer, on atactic polypropylene and on acompatible tackifying resin, optionally in the presence of aplasticizing oil and/or of a wax originating from petroleum and/or of astabilizer.

U.S. Pat. No. 4,939,202 proposes a moisture-resistant adhesivecontaining a propylene-based amorphous polymer, a propylene-basedcrystalline polymer and a petroleum resin containing hydrocarbonscontaining from 4 to 10 carbon atoms.

U.S. Pat. No. 4,149,741 employs a hot-metal adhesive including astyrene-isoprene-styrene block copolymer, a compatible tackifying resin,a plasticizing oil and a stabilizer and, optionally, a wax derived frompetroleum.

Catamenial liners, for their part, generally include an absorbent fillerof the cellulose fluff or superabsorbent type and a covering based on anonwoven fabric made of polypropylene or of viscose, to the outer faceof which covering an adhesive composition is applied allowingpositioning on the undergarment. To manufacture such liners thecompositions described in the following documents have been proposed.

EP 0104005-A proposes an adhesive based on a viscoelastic elastomer ofA-B-A type (in which B denotes a polyolefin, for example anethylene-butylene copolymer and A includes a polystyrene), and on atackifying resin.

Finally, in WO 93/10734 a composition is described including a copolymerof formula (A-B)_(n)-Y (in which Y is a multivalent coupling agent, A isa vinyl monomer substituted by an aromatic radical and B ispolybutadiene), a compatible tackifying resin and a plasticizing oil.

The adhesives of the prior art which have just been mentioned are notentirely satisfactory in the field of hygiene.

Thus, in the case of disposable nappies, the polypropylene-basedhot-melt adhesives (U.S. Pat. No. 4,460,728 and U.S. Pat. No. 4,939,202)are difficult to use in conventional devices operating by fiberizing orspraying, and the compositions described in U.S. Pat. No. 4,526,577 andU.S. Pat. No. 5,149,741 exhibit poor behaviour towards water, which canresult in particular in the separation of the absorbent filler adjoiningthe leakproof film.

In the case of catamenial liners the abovementioned adhesivecompositions are found to be satisfactory when applied to a coveringmade of nonwoven fabric. However, it is found that the said compositionsare not suited for the preparation of latest-generation ultrafine linerswhich comprise a covering consisting of a polyethylene-based open-workedor perforated film. It is found, in fact, that the use of compositionsbased on ethylene-vinyl acetate copolymer results in soiling of thecovering and that the adhesives according to EP 0 104 005-A and WO93/10734 must be applied at an elevated temperature, of the order of 150to 180° C., in order to adhere to the support in a satisfactory manner.

DESCRIPTION OF THE INVENTION

New pressure-sensitive thermoplastic adhesive compositions have now beenfound which do not exhibit the abovementioned disadvantages, thesecompositions being characterized in that they include

a) at least one ethylene-alkyl acrylate copolymer

b) a tackifying resin

c) optionally a diluent and/or a stabilizer and/or a wax.

The ethylene-alkyl acrylate copolymer according to the invention isgenerally chosen from copolymers containing from 15 to 45% andpreferably 25 to 35% by weight of alkyl acrylate.

The alkyl acrylate is advantageously chosen from methyl acrylate, butylacrylate and 2-ethylhexyl acrylate. Butyl acrylate is preferablyemployed.

Such copolymers which exhibit a melt index of between 0.5 and 1000 andpreferably 2 and 500 are generally employed.

Among the abovementioned copolymer mixtures which can be employed it ispossible to mention very particularly the mixtures based on copolymerexhibiting an acrylate content of between 15 and 40%, preferably 30 and35, and a melt index of between 500 and 2, preferably 320 and 2.

The tackifying resin according to the invention is chosen from the groupconsisting of solid or liquid hydrocarbon resins such as theunhydrogenated or completely or partially hydrogenated aliphatic oraromatic resins, for example ESCOREZ 5300 form Exxon and IMARV S 100 Sform Idemitzu, resins based on natural or modified, for examplepolymerized, rosin esters, especially pentaerythritol or glycerolesters, for example UNITAC R 100 L form Union-Camp, polyterpene ormodified polyterpene resins, for example WINGTACK from Goodyear and“-methylstyrene resins, for example URATACK 68520 from DSM.

The diluent according to the invention is chosen from aliphatic ornaphthenic oils, plasticizers such as phthalates, adipates andbenzoates, oligomeric or polymeric olefins of low molecular weight,polypropylene, polybutene and hydrogenated polyisoprene.

The wax according to the invention is generally chosen from waxes ofpetroleum origin or from Fischer Tropsch synthesis.

The stabilizer according to the invention is generally chosen fromantioxidants such as substituted phenols, for example IRGANOX 1076 fromCiba-Geigy and phosphites.

The pressure-sensitive hot-melt adhesive composition in accordance withthe invention generally includes from 20 to 50% by weight, andpreferably 30 to 40%, of ethylene-alkyl acrylate copolymer, from 30 to80% by weight, and preferably 40 to 60%, of tackifying resin, from 0 to35% by weight, and preferably 10 to 25%, of diluent, from 0 to 1.5% byweight of stabilizer and from 0 to 15% by weight of wax.

Compositions according to the invention advantageously exhibit aviscosity of between 1000 and 10,000 mPa s (Brookfieldviscometer—temperature 150-170° C.).

The compositions in accordance with the invention are generally obtainedby mixing at a temperature which varies from 120 to 170° C.

The compositions thus obtained exhibit good adhesive to polyolefinicsupports such as films and nonwoven fabrics made of polyethylene orpolypropylene, good cohesion and good water resistance. In addition,these compositions can be processed very easily according to thetechniques in the field of hygiene, in particular by coating,fiberizing, spraying or control-coating.

The pressure-sensitive hot-melt adhesive compositions according to theinvention are particularly recommended for the manufacture of articlesrelated to the field of hygiene, especially of disposable nappies and ofcatamenial liners, which articles also constitute a subject-matter ofthe invention. These compositions are advantageously used to manufacturenappies comprising one or more elastic or non-elastic synthetic films ofvaried nature, for example such as those used to obtain an elasticwaistband. They can, in addition, be used to stabilize and fix theabsorbent filler, which is generally based on cellulose wool (“fluff”).

EXAMPLES

The examples which follow make it possible to illustrate the invention.Examples 1 to 8 and 12 relate to disposable nappies and Examples 9 to 11concern catamenial liners.

Example 1

Into a mixer maintained at 130° C. are added 103 g of dioctyl phthalate,400 g of ethylene-butyl acrylate copolymer (Lotry® 35 BA 320; butylacrylate: 35%; melt index: 320; Elf Atochem S.A. ), 490 g of tackifyingresin ESCOREZ 6372; Exxon) and 0.7 g of antioxidant (IRGANOX 1010;Ciba-Geigy). After complete homogenization a hot-melt composition isobtained exhibiting a Brookfield viscosity of 4500 mPa s at 150° C.

The composition thus obtained is deposited by fiberizing on apolyethylene film at a rate of 10 g/m². The lining is performed, on theone hand, on a nonwoven fabric made of polypropylene and, on the otherhand, on a polyethylene film.

The measurements obtained after application of the 180° peel test at 200mm/min are 4 N/25 mm and 4.4 N/25 mm in the case of thepolyethylene/nonwoven and polyethylene/polyethylene materialsrespectively.

Example 2

The operation is carried out in the conditions of Example 1 in thepresence of 65 g of polybutene (Napvis 10; BP), 300 g of ethylene-butylacrylate copolymer (lotry® 35 BA 320; butyl acrylate: 35%; melt index:320; Elf Atochem S.A.), 40 g of ethylene-butyl acrylate copolymer(Lotry® 30 BA 02; butyl acrylate: 30%; melt index: 2; Elf Atochem S.A.),455 g of tackifying resin ESCOREZ 5320; Exxon), 45 g of wax (25 B;Total) and 5 g of stabilizer (IRGANOX 1010; Ciba-Geigy).

The adhesive thus obtained is deposited by coating onto a polyethylenefilm over a width of 25 mm at a rate of 5 g/m². The lining is performedin the conditions of Example 1.

The measurements obtained after application of the 180° peel test at 200mm/min are 2.7 N/25 mm and 2.3 N/25 mm in the case of thepolyethylene/nonwoven and polyethylene/polyethylene materialsrespectively.

Example 3 (Comparative)

The operation is carried out in the fiberizing conditions according toExample 1 in the presence of a hot-melt adhesive based on APAO (TH 706;CECA S.A.).

The composition thus obtained can be fiberized only in conditions wherethe temperature is higher than 170° C. and the air pressure is higherthan 5 bar (5 H 10⁵ Pa).

Example 4

The operation is carried out in the fiberizing conditions according toExample 1 in the presence of the hot-melt adhesive of Example 2.

It is seen that the composition is completely fiberizable in theconditions of application (temperature: 140° C.; air pressure: 1.5 bar(1.5 H 10⁵ Pa)).

Example 5 (Comparative)

The procedure follows the coating conditions of Example 2, modified inthat a hot-melt adhesive based on APAO (TH 706; CECA S.A.) is employed.

The measurements obtained after application of the 180° peel test at 200mm/min are 2.5 N/25 mm and 2.1 N/25 mm in the case of thepolyethylene/nonwoven and polyethylene/polyethylene materialsrespectively.

Example 6

The hot-melt adhesive according to Example 1 is applied to apolyethylene film at a rate of 5 g/m² and lamination onto a pad of fluff(cellulose wool) is performed.

The material thus obtained is soaked over an area of 20 cm H 20 cm withthe aid of 100 ml of water. After 10 minutes the fluff is scratchedmanually. It is seen that the adhesive-coated area of the polyethyleneremains covered with a film of fluff.

Examples 7 and 8 (Comparative)

The procedure follows the conditions of Example 6 in the presence of arubber adhesive containing 25% by weight of styrene-butadiene-styrene(Example 7) or styrene-isoprene-styrene (Example 8) polymer, 55% byweight of petroleum resin and 20% by weight of naphthenic oil. It isseen that the adhesive-coated area of the polyethylene does not remaincovered with a film of fluff after scratching.

Example 9

150 g of naphthenic oil (NYTEX 820; Nynas) are introduced into a mixerwhich is heated to 130° C. The following are added: 220 g ofethylene-butyl acrylate copolymer (lotry® 35 BA 320; butyl acrylate:35%; melt index: 320; Elf Atochem S.A.), 60 g of ethylene-butyl acrylatecopolymer (lotry® 30 BA 02; butyl acrylate: 30%; melt index: 2; ElfAtochem S.A.), 348 g of resin (ECR 395; Exxon), 100 g of tackifyingresin (OULUPALE B 100; Forchem), 120 g of tackifying resin (URATACK69540; DSM) and 0.2 g of stabilizer (IRGANOX 1010; Ciba-Geigy).

The composition thus obtained, which exhibits a viscosity of 3470 mPa sat 150° C., is applied by coating at 130° C. onto silicone-treated paper(25 mm width) and transferred onto a polyethylene film.

The adhesiveness, measured according to NF standard Q 34013, is 2.0 N/25mm.

No soiling is seen on the support.

Examples 10 and 11 (Comparative)

The conditions of Example 9 are followed in the presence of an adhesive,on the one hand, based on ethylene-vinyl acetate copolymer (XT 7117;CECA S.A.) and, on the other hand, based on styrene-butadiene-styrenecopolymer (TH 712; CECA S.A.), the latter being applied at 160° C.(limiting temperature for the coating).

The adhesiveness is equal to 1.7 N/25 mm and 2.0 N/25 mm respectively.

Traces of soiling are seen on the support with the XT 7117 adhesive(Example 10).

A deterioration of the support is seen in the presence of the TH 712adhesive (Example 11), due to the high application temperature.

Example 12

The process is performed under the conditions of Example 1 modified inthat an ethylene/methyl acrylate copolymer (Lotryl® 28 MA 175; 28%methyl acrylate; melt index 175; Elf Atochem S.A.) is used.

After homogenization, a self-adhesive hot-melt composition is obtained.This composition is deposited by fiberizing according to the method ofExample 1, the lining being performed on a nonwoven fabric made ofpolypropylene.

The measurement obtained after applying the 180° peel test at 200 mm/minis equal to 3.5 N/25 mm.

Although the invention has been described in conjunction with specificembodiments, it is evident that many alternatives and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, the invention is intended to embrace all ofthe alternatives and variations that fall within the spirit and scope ofthe appended claims. The above references are hereby incorporated byreference.

What is claimed is:
 1. Pressure-sensitive hot-melt adhesive compositioncomprising: a) at least one ethylene-alkyl acrylate copolymer, b) atackifying resin, c) optionally a diluent, a stabilizer, or a wax andmixture thereof, wherein said adhesive composition is capable of beingused in fiberizing or spraying devices, wherein said adhesivecomposition can be coated onto a support at a temperature less than 150°C., and wherein said adhesive composition does not soil said supportwhen said adhesive composition is coated onto said support. 2.Composition according to claim 1, wherein the ethylene-alkyl acrylatecopolymer contains from 15 to 45% by weight of alkyl acrylate. 3.Composition according to claim 1, wherein the alkyl acrylate is selectedfrom methyl acrylate, butyl acrylate and 2-ethylhexyl acrylate. 4.Composition according to claim 1, wherein the copolymer exhibits a meltindex of between 0.5 and
 1000. 5. Composition according to claim 1,wherein it exhibits a viscosity of between 1000 and 10,000 mPa s attemperatures from 150 to 170° C.
 6. Composition according to claim 1,wherein it includes: from 20 to 50% by weight of ethylene-alkyl acrylatecopolymer, from 30 to 80% by weight of tackifying resin, from 0 to 35%by weight of diluent, from 0 to 1.5% by weight of stabilizer, and from 0to 15% by weight of wax.
 7. Method for manufacture of articles intendedfor hygiene, containing at least one polyolefinic support comprisingpreparing said articles by adhesively bonding constituents of saidarticles with a composition, wherein said composition is apressure-sensitive hot-melt adhesive composition comprising: a) at leastone ethylene-alkyl acrylate copolymer, b) a tackifying resin, and c)optionally a diluent, a stabilizer, or a wax and mixtures thereof,wherein said adhesive composition is capable of being used in fiberizingor spraying devices, wherein said adhesive composition can be coatedonto a support at a temperature less than 150° C., and wherein saidadhesive composition does not soil said support when said adhesivecomposition is coated onto said support.
 8. Method according to claim 7,wherein the articles are disposable diapers or catamenial liners. 9.Disposable diaper enclosing a composition, wherein said composition is apressure-sensitive hot-metal adhesive composition comprising: a) atleast one ethylene-alkyl acrylate copolymer, b) a tackifying resin, andc) optionally a diluent, a stabilizer, or a wax and mixtures thereof,wherein said adhesive composition is capable of being used in fiberizingor spraying devices, wherein said adhesive composition can be coatedonto a support at a temperature less than 150° C., and wherein saidadhesive composition does not soil said support when said adhesivecomposition is coated onto said support.
 10. Catamenial liner enclosinga composition, wherein said composition is a pressure-sensitive hot-meltadhesive composition comprising: a) at least one ethylene-alkyl acrylatecopolymer, b) a tackifying resin, and c) optionally a diluent, astabilizer, or a wax and mixtures thereof.